Electricity and Circuits Flashcards
In the atom, which particles can be found in the nucleus and which can be found orbiting the nucleus?
Protons and neutrons are in the nucleus, electrons orbit around the nucleus.
Conventional current goes:
From positive to negative
Electrons flow:
From negative to positive
In this type of circuit there is just one route the current can take around the circuit. Components cannot be switched on and off separately.
Series circuit
In this type of circuit there are junctions that allow the current to take different routes. Components can be switched on and off separately.
Parallel circuit
What component is represented as a symbol with a X in?
A light bulb
What component is represented as a symbol with an A in?
An ammeter
What component is represented as a symbol with a V in?
a voltmeter
Where in a circuit should an ammeter be placed?
in Series with the component
Where in a circuit should a voltmeter be placed?
in Parallel with the component
Current is measured in
Amps (A) (also called Amperes)
Voltage (aka Potential difference) is measured in
Volts (V)
What happens to the current that flows into a junction?
Current is conserved - current splits at a junction to travel along different branches, but the total amount entering the junction is the same as the total amount leaving.
In a parallel circuit, the total ____________________ across each branch of the circuit is the same. When there is more than one component in each branch of a circuit the ______________________ across all the components add up to give the total supplied by the cell or battery.
Potential difference, or voltage, in Volts.
What is the equation that links Charge, Current, and time
Charge (C) = Current (A) x time (s)
Q = I x t
What is the unit for Charge?
Coulombs (C)
What electrical quantity is represented by the letter Q?
Charge
What electrical quantity is represented by the letter I?
Current
What is the equation that relates electric charge, potential difference and energy transferred in a circuit?
Energy transferred (J) = charge moved (Q) x potential difference (V)
What is electrical resistance?
The opposition to the flow of electrons. It is measured in ohms (symbol is a Greek letter omega Ω)
What is the equation that links voltage, current and resistance?
Voltage (V) = current (A) x resistance (Ω)
What happens to total resistance if you combine two resistors in series?
The total resistance is the sum of the individual resistances
What happens to total resistance if you combine two resistors in parallel?
The total resistance is always less than either of the individual resistances
This component is non-ohmic. The resistance is very high when the current flows in the negative direction, but low when the current flows in the positive direction.
Diode
This component is non-ohmic. The resistance increases as the potential difference increases. The graph is an ‘s’ shape.
Filament lamp/light bulb
This component is non-ohmic. the graph is a ‘ski-slope’ shape. The resistance varies with light intensity.
LDR or Light-dependent resistor
This component is non-ohmic. the graph is a ‘ski-slope’ shape. The resistance varies with light temperature.
Thermistor
What do B.I.R.D and T.U.R.D stand for when referring to non-ohmic components
Brightness Increases Resistance Decreases (for LDRs)
Temperaure Up Resistance Down (for Thermistors)
Why do electrical wires get hot?
When a current passes through a wire energy is transferred because work is done against the resistance.
When energy is transferred due to heating, and spreads out to give the surroundings thermal energy we say it is:
dissipated
Give an example where the heating effect of a current is useful:
Toaster, kettle, hair dryer, electric heater - anything with a heating element.
Give an example where the heating effect of a current is not useful:
A Computer, Plugs & Wires - any electronic device that is not meant to get hot.
Resistance can be reduced by:
Using wires made from metals with low resistance e.g. copper or aluminium.
Using a thicker wire (larger diameter).
Cooling metals so the lattice ions are not vibrating as much.
Describe what happens to electrons as they flow through a lattice of positive ions within a wire or component.
As electrons flow through the lattice of vibrating ions within a wire/component they collide with the ions. The more collisions the higher the resistance. When the electrons collide with the ions, they transfer energy to them making them heat up (and vibrate more!)
What is the equation for calculating electrical energy in terms of current, voltage and time?
E = I t V
Electrical energy (J) = Current (A) x voltage (V) x time (s)
What is power and what units are used to measure it?
Power is the energy transferred per second, measured in Watts (W)
What is the equation that relates power to energy used in joules?
P=E/t
Power (Watts) = Energy transferred (J) / time taken (s)
How can you calculate power when you know current, potential difference and/or resistance?
P = I x V
Power (W) = current (A) x voltage (v)
and
P= I2 x R
Power (Watts) = Current squared (Amps squared) x Resistance (Ohms)
What is the voltage supply and frequency of the UK domestic electricity supply (mains)?
230V
50Hz
What is alternating current?
Current keeps alternating direction - with a frequency of 50 Hz for the UK mains supply.
Compare a.c. and d.c. in terms of voltage.
in d.c. the voltage remains constant.
In a.c. the voltage also changes - increasing to a peak voltage, then decreasing to zero before increasing to a peak negative voltage (opposite direction) then back to zero. On repeat.
What type of voltage (alternating/direct) is supplied by the mains, and what is supplied by a battery or cell?
Mains = alternating
Battery/cell = direct
How does a fuse work?
A fuse is a tube with a thin wire inside. The current passes through the wire and the wire gets hotter. If the current exceeds a certain value the wire melts. This breaks the circuit and stops the current. They must then be replaced.
What colour is the Earth wire and what voltage does it carry if the circuit is correctly connected?
Green and yellow.
It is for safety and is at 0V if the circuit is correctly connected.
What colour is the Live wire and what voltage does it carry if the circuit is correctly connected?
Brown.
It connects the appliance to the mains supply. Voltage is 230V.
What colour is the Neutral wire and what voltage does it carry if the circuit is correctly connected?
Blue.
It is the return path to the power station. It carries 0V.
